1) Field of the Invention
The present invention relates to a vacuum processing device that is used to process a substrate-like wafer such as a semiconductor wafer and a liquid crystal display, and performs processes such as fine patterning using a plurality of types of gas, and a method of transporting a sample that is a process subject in the vacuum processing device.
2) Description of the Related Art
A vacuum processing device includes a processing unit including a vacuum container having a vacuum process chamber therein, an evacuation device, a plasma forming device and the like, and productivity is required to be improved with lower costs for such a vacuum processing device. It is an important task to make process efficiency per device higher by improving throughput (the number of substrates processed per unit time) as a representative example of productivity indices. In the following, a semiconductor processing device is explained as an example just like a sample to be a process subject in a vacuum processing device is called a wafer, but the present invention is not limited to a semiconductor processing device. Also, although throughput is explained as a representative example of productivity indices, the same applies to another productivity index such as a turn-around time, and the present invention is not limited to throughput.
In a process of a semiconductor processing device which is one application a vacuum processing device, there is a step of a process performed on a wafer such as a semiconductor wafer that is a process subject wafer under vacuum such as a plasma process including an etching process, and in order to perform such a process with high throughput, namely to improve process efficiency per device, a semiconductor processing device in which a plurality of process chambers is installed is used. Normally, a known semiconductor processing device includes a vacuum process chamber and an atmospheric transport chamber that is under a normal pressure.
A cassette (FOUP) that houses a predetermined number of wafers, for example 25, is attached to a front surface side of the above-described semiconductor processing device, a transportation robot takes out wafers from the cassette one by one to transport the wafers to a load lock to switch from atmospheric pressure to vacuum, the wafers are carried from the load lock in which pressure is reduced by vacuum evacuation into any of vacuum process chambers where a process is performed via a transportation path with reduced pressure, and then the process is performed. When the process ends, the wafers are carried out to go through the path that the wafers went through when they were carried in in a reverse direction to return to a space under atmospheric pressure via the load lock. Thereafter, the wafers return to the same positions in the same cassette where the wafers were before they were carried out by the transportation robot. This is a general order of actions when a semiconductor processing device processes a wafer.
As such a semiconductor processing device, a device with a structure called a cluster tool in which a vacuum process chamber is connected radially around a transport chamber is widely used. However, the cluster tool device requires a large installation area, and in particular with an increase in diameters in recent years, the installation area has been becoming larger and larger. To cope with the problem, a device with a structure called a linear tool has appeared to realize both a smaller installation area and improved throughput. A characteristic of the linear tool is that it has a plurality of transport chambers, a vacuum process chamber is connected to each transport chamber, and the transport chambers are mutually connected directly or interposing spaces for passing wafers (hereinafter, buffer room) therebetween.
The linear tool has a mechanism that allows transportation of wafers by a plurality of transportation robots to a plurality of vacuum process chambers in parallel by including the plurality of transportation robots the number of which used to be one in a conventional semiconductor processing device, thus realizing high throughput.
Although a structure of the linear tool that realizes improvement of throughput while making an installation area smaller has been proposed, a technique for shortening process time and making transportation efficient is also important for throughput improvement. However, transportation control having been applied to a cluster tool is targeted at a single transportation robot, and when the transportation control is applied as it is for a linear tool including a plurality of transportation robots, throughput is lowered in some cases.
As a representative method of transportation control in a cluster tool, there is a procedure of control by transporting wafers to process chambers starting in order with those where processes have ended earlier. When the procedure is applied to a linear tool, it is possible to realize high throughput if process time required for processing wafers is approximately the same for process chambers. However, if different types of products are processed in parallel in process chambers, process time in each process chamber depends on the type of a product, and timing at which each process ends differs often.
In such a situation, it may be possible to conceive of simply transporting a next wafer just after a process in a process chamber among a plurality of process chambers ends. At this time, when process time of a wafer to be transported next to a process chamber where a process has ended is long, although it may depend on the number and arrangement of process chambers in the semiconductor processing device, a transportation path for a wafer planned to be processed in a process chamber whose process time is short may be blocked, meaning that the wafer should have been transported to the process chamber beforehand. As a result, throughput is lowered.
One effective means to improve throughput of a vacuum processing device in which a plurality of process chambers is installed is to disperse loads of transportation robots. For this purpose, Japanese Patent Application Laid-Open Publication No. 2009-94530 discloses that higher throughput as compared with a conventional vacuum processing device is realized by providing a plurality of transportation robots the number of which used to be one in the conventional device, and transporting wafers to a plurality of vacuum process chambers in parallel. However, regarding a section to control the plurality of transportation robots, Japanese Patent Application Laid-Open Publication No. 2009-94530 only mentions that the transportation robots pass wafers among them. In an actual operation of a semiconductor processing device, process time in a process chamber differs depending on a wafer processed in the process chamber. Also, for this reason, a transportation control procedure of transporting wafers simply to process chambers starting in order with those where processes have ended earlier in a linear tool including a plurality of transportation robots has a problem that throughput is lowered in some cases depending on process time of wafers processed in each process chamber.
Also, an efficient transportation method differs depending on a step of a process on a wafer in some cases. One process step may complete by a single process in a process chamber, and another process step may complete by performing processes a plurality of times. Furthermore, an efficient transportation method differs depending on operation conditions. Under one operation condition, a process chamber where a wafer is planned to be processed may be changed freely at any time, and under another operation condition, a process chamber where a process is planned may not be changed once transportation of a wafer is started from an initial position. The operation condition that a process chamber where a wafer is planned to be processed is changed freely at any time means that process conditions such as types of gas to be used in processes are the same for a plurality of process chambers, and quality of a wafer after a process is not affected no matter in which process chamber the wafer is processed. Also, the operation condition that a process chamber where a process is planned may not be changed once transportation of a wafer is started from an initial position means that although process conditions such as types of gas to be used in processes are the same for a plurality of process chambers, an 121 of minute adjustment of process conditions according to a wafer-specific state such as film thickness is performed once a process chamber where a wafer is planned to be processed is decided or process conditions such as types of gas to be used in processes are different for process chambers.